code: def test_validate_filter_is_not_null(self):
      filters = [["a", "is not null"]]
      assert validate.validate_filter(filters) == filters
  
file_path: perspective/python/perspective/perspective/tests/viewer/test_validate.py
imports: from pytest import raises
  from perspective.core import PerspectiveError
  from perspective.core import Plugin
  import perspective.viewer.validate
  from perspective.core._version import __version__
label_desc: Use image node_id 9 for calling the TestValidate obj's underlying member method code with example usage: obj.test_validate_filter_is_not_null() without return types